The objective of this proposal is to exploit the unique advantages offered by gene fusions to study various aspects of ribosomal RNA genetics and control. The fusion of two different operons has provided an added dimension to the selective techniques available to the molecular geneticist and has provided a facile means of observing the regulation of genes specifying products which are not readily measured. The advent of restriction endonuclase and recombinant DNA technology makes possible the assembly of genetic information from a variety of sources in a highly controlled fashion. We have constructed a gene fusion between a ribosomal RNA operon control region (rrnCR) and the well characterized tryptophan operon. With this fusion we propose to: (a) study the influence of various treatments on a single ribosomal control region, (b) apply selective pressure for isolation of mutants either in the rrn control region or in other genes which interact with it and (c) study and manipulate the control region in vitro. It will further allow us to investigate the mechanism of any molecular interactions with the ribosomal control region. Although it has been assumed that the several ribosomal cistrons in E. coli are identical, that assumption must now be questioned. We plan to compare the DNA sequence of a number of rrn control regions in an effort to pinpoint and quantify any heterogeneity in control regions. If differences are found the cistrons will be compared, using fusion studies, both in vivo and in vitro. Any observed differences in a control region will be correlated to overall heterogeneity in control regions. If differences are found the cistrons will be compared, using fusion studies, both in vivo and in vitro. Any observed differences in a control region will be correlated to overall heterogeneity in the remainder of the rrn cistron. DNA sequencing is used to plan fusion schemes, to identify the cloned fusion sequence and to determined precise differences between wild type and mutant rrnCR alleles.